|Budget Amount *help
¥3,400,000 (Direct Cost : ¥3,400,000)
Fiscal Year 1999 : ¥1,500,000 (Direct Cost : ¥1,500,000)
Fiscal Year 1998 : ¥1,900,000 (Direct Cost : ¥1,900,000)
To explore the regulation mechanism of chloroplastic ascorbate peroxides (chlAPX) isoenzymes, we studied the following heads,
(1) We have previously shown that stromal (sAPX) and thylakoid-bound (tAPX) ascorbate peroxidase isoenzymes of spinach chloroplasts arise from a common pre-mRNA by alternative splicing. To explore the production of mature, functional mRNA encoding chlAPX isoenzymes, mRNA analysis were performed. Four mRNA variants, one form (tAPX-1) for tAPX and three forms (sAPX-I, -II, and -III) for sAPX, were identified. The expression levels of mRNA variants for sAPX and tAPX isoenzymes are in nearly equal quantities throughout the spinach leaves grown under normal conditions.
(2) We studied the response of each APX isoenzyme in spinach leaves under stress conditions imposed by high-light intensity, drought, salinity, and applications of paraquat and abscisic acid. The steady-state transcript level of cytosolic APX (cAPX) remarkably increased in response to high-light intensity and paraquat treatment. The cAPX activity increased in parallel with its transcript abundance during high-light intensity. The other isoenzymes showed no significant changes in their transcript an protein levels and activities, except for he gradual decrease in the chlAPX isoenzymes activities.
(3) A cDNA clone encoding L-galactono- γ-lactone (GAL) dehydrogenase was isolated from tobacco leaves. The cDNA clone contained the protein of 56,926 Da, preceded by a putative mitochondrial targeting signal. In fact, GAL dehydrogenase was localized in the mitochondria of tobacco cells. GAL dehydrogenase mRNA is expressed in the leaves, stems, and roots in almost equal quantities. The partially purified recombinant enzyme was used for comparative studies on the native enzymes from tobacco and other sources ; The enzymatic properties of recombinant GAL dehydrogenase were similar to those of other GAL dehydrogenases.